The current invention relates to treatment of cerebral swelling as well as regulation of the temperature in the brain and spinal cord. The invention relates to a method and apparatus for altering the temperature of the brain surface and/or the cerebrospinal fluid in the ventricles of the brain and surrounding the spinal cord.
Hypothermia has been shown to provide cerebral and spinal cord injury protection from either trauma, ischemia, or hypoxia. Ischemia may occur from cardiac arrest, cardiac failure, stroke, head or spinal cord injury, aneurysm surgery, cardiac surgery, and aortic or carotid surgery. Hypothermia is also effective in reducing increased intracranial pressure from cerebral swelling. The mechanisms involved in hypothermic cerebral protection are several-fold and include 1) reduction in cerebral glucose and oxygen metabolism and decreasing lactate content following injury, 2) preventing disruption of the blood brain barrier and consequently reducing cerebral edema, 3) reduction of endogenously toxic neurotransmitters like glutamate, glycine, aspartate, acetylcholine, and norepinephrine into the brain after injury, 4) inhibit excessive calcium entry and intracellular calcium overload into neurons, 5) protecting membrane structural proteins like microtubule-associated protein-2, and 6) preventing diffuse axonal injury following brain trauma.
In general, the human brain and spinal cord are maintained at a constant temperature of approximately 37 to 38 degrees celsius. Hypothermia is considered mild when the body temperature is 33 to 35 degrees celsius, moderate between the temperatures of 28 to 32 degrees, and severe in the temperature range of 24 to 28 degrees celsius. Most studies in humans have involved mild to moderate systemic hypothermia mainly because of the significant side effects that occur from induced systemic hypothermia. These include infection, cardiac arrhythmias, coagulopathy, renal failure, as well as rewarming shock. In order to avoid these complications the degree and duration of hypothermia has been shortened thereby limiting its effectiveness.
Generally, cooling of the brain has been accomplished through whole body cooling with use of a cooling blanket, immersing the patient in ice, or cooling the blood through a cardiopulmonary bypass machine. A few methods have been described regarding selective brain and spinal cord hypothermia. These involve cooling the arterial vessel or blood supply to the brain or external cooling helmets, each with its own significant limitations.
Several catheters have been developed to induce systemic hypothermia by inserting them into the bloodstream. More recently catheters have been developed that can be inserted into the arterial vessels to the brain to induce selective brain hypothermia. These catheters are limited in their size and functionality by the small vessel lumen as well the inability to cool all the four major arterial vessels supplying blood to the brain and are unable to cool the spinal cord via this methodology. They also carry the risk of ischemic and thromboembolic stroke by either impairing the blood flow to the brain or dislodging clots that can develop in intra-arterial catheters.
External cooling helmets have limited effectiveness since the blood to the cooled scalp does not circulate into the brain and returns systemically which along with the thick skull dilutes the hypothermic effect to the brain.
Selective brain and spinal cord cooling with insertion of catheters or templates into the ventricular, subdural or epidural space is a novel concept. This avoids the side effects and complications seen from other methods of cooling.
The invention provides a method and apparatus for performing selective hypothermia to the brain and/or the spinal cord for injury protection without the need for systemic cooling.
For selective brain cooling, in one embodiment of the present invention, a flexible catheter is inserted into the cerebral lateral ventricle to cool the cerebrospinal fluid and henceforth the brain. The catheter has three lumens with a distal heat conductive element which also has holes to allow for drainage of cerebrospinal fluid. The inner-most lumen is connected with the outer-most lumen at the tip of the catheter and allows for circulation of a coolant. The intermediate lumen has holes at the distal end that allows for drainage of cerebrospinal fluid as well as intracranial pressure monitoring similar to a ventriculostomy. An occipital approach to the placement of the catheter is preferred to allow for a longer catheter with more surface area for heat exchange. In another embodiment of this catheter, the inner-most lumen allows for drainage and the intermediate lumen is connected with the outer lumen for circulation of the coolant.
For selective spinal cord cooling, in another embodiment of the catheter described above, a catheter with a longer distal heat conductive element is inserted into the lumbar subdural or epidural space to allow for cooling around the spinal cord. This catheter may or may not have a lumen for drainage of cerebrospinal fluid.
In another embodiment for selective brain cooling, a larger surface area template is inserted into the subdural space either through a burr-hole or following a craniotomy. These templates have variable sizes with small thickness and circulate a coolant with a wider surface area to allow placement in the subdural space to directly cool the brain surface. These templates can also be placed in the epidural space of the spine for selective spinal cord cooling.
The catheters and templates are designed to allow an inert coolant to circulate in the lumens without direct exposure to the brain or spinal cord and thereby altering the brain or spinal cord temperature. This allows for selective cooling of the brain and spinal cord for treatment of injury from trauma, ischemia, hypoxia and/or cerebral swelling. The length and size of the catheters and templates is variable to allow for a wide selection and patient individuality.